fix(SM-19): restore module-alias narrowing and constructor disambiguation

Codex adversarial review on PR #770 surfaced two silent regressions in the
SM-19 thin dispatcher:

Finding 1 [high] — Typed member calls bypassed module-alias narrowing.
When two homonym receiver types are both imported by the caller, the
import-scoped tier no longer narrows and the owner/file resolvers see
genuine ambiguity. The dispatcher null-routed silently, dropping valid
CALLS edges. Fix: consult `resolveModuleAliasedCall` at the top of the
typed-member branch so an active alias on `call.receiverName` picks the
aliased file before the generic resolvers run.

Finding 2 [medium] — Constructor dispatch lost overload disambiguation.
When `resolveStaticCall` bails (ambiguous or ownerless Constructor pool)
and the caller supplied `overloadHints` / `preComputedArgTypes`, the
branch fell straight through to `singleCandidate` — which also bails on
multiple same-arity survivors. Fix: between `resolveStaticCall` and
`singleCandidate`, run constructor-filtered overload disambiguation on
the tiered pool. Only engages when a narrowing signal is present;
preserves SM-10 R3 null-route for genuinely ambiguous cases.

Tests:
- call-processor.test.ts: 3 new dispatcher-level regression tests
  covering real-homonym alias narrowing, constructor overload
  disambiguation with `argTypes`, and null-route control
- symbol-table.test.ts: update `module alias homonyms` test which
  previously codified the Finding 1 regression; now asserts resolution
  to the aliased file's method

Verification: 3191 unit + 2398 integration tests pass; tsc --noEmit
clean; prettier clean.

gitnexus/src/core/ingestion/call-processor.ts

@@ -1687,12 +1687,43 @@ const resolveCallTarget = (
     );
   }
   if (call.callForm === 'constructor') {
-    return (
+    const staticResult = resolveStaticCall(
-      resolveStaticCall(call.calledName, currentFile, ctx, call.argCount, tiered) ??
+      call.calledName,
-      singleCandidate(tiered, call.argCount, 'constructor')
+      currentFile,
+      ctx,
+      call.argCount,
+      tiered,
     );
+    if (staticResult) return staticResult;
+
+    // Codex SM-19 Finding 2: When `resolveStaticCall` bails on ambiguous or
+    // ownerless Constructor pools, give overload/arg-type disambiguation a
+    // chance before null-routing. Only engages when the caller supplied a
+    // narrowing signal — preserves SM-10 R3 for genuinely ambiguous cases.
+    if (overloadHints || preComputedArgTypes) {
+      const ctorPool = filterCallableCandidates(tiered.candidates, call.argCount, 'constructor');
+      if (ctorPool.length > 1) {
+        const disambiguated = overloadHints
+          ? tryOverloadDisambiguation(ctorPool, overloadHints)
+          : preComputedArgTypes
+            ? matchCandidatesByArgTypes(ctorPool, preComputedArgTypes)
+            : null;
+        if (disambiguated) return toResolveResult(disambiguated, tiered.tier);
+      }
+    }
+    return singleCandidate(tiered, call.argCount, 'constructor');
   }
   if (call.receiverTypeName) {
+    // Codex SM-19 Finding 1: Consult module-alias narrowing BEFORE the
+    // owner-scoped / file-scoped resolvers. When the caller imports two
+    // homonym receiver types from different files, import-scoped tiering
+    // does not narrow (both files are in scope) and the owner/file fallback
+    // sees genuine ambiguity. An active module alias on `call.receiverName`
+    // is the only remaining disambiguation signal; without this call the
+    // dispatcher null-routes silently and drops a valid CALLS edge.
+    const aliasResult = resolveModuleAliasedCall(call, currentFile, ctx, widenCache, tiered);
+    if (aliasResult) return aliasResult;
+
     // Skip the owner-scoped MRO path when the tiered pool has genuine
     // overload ambiguity that needs D1-D4+E handling, not D0.
     const skipMember =

gitnexus/test/unit/call-processor.test.ts

@@ -2493,6 +2493,152 @@ describe('processCalls — D0 MRO fast path (SM-10)', () => {
     expect(authSave).toBeDefined();
     expect(userSave).toBeUndefined();
   });
+
+  it('module-alias guard (real homonym): both files imported, alias narrows typed member call to aliased file', async () => {
+    // Codex SM-19 adversarial review Finding 1: When BOTH homonym files are
+    // imported by the caller, import-scoped tiering no longer narrows the
+    // tiered pool — the dispatcher sees two `save` candidates. Module-alias
+    // narrowing is the only remaining disambiguation signal. The typed-member
+    // branch must consult the alias map or null-route silently.
+    const authModFile = 'src/auth_mod.py';
+    const userModFile = 'src/user_mod.py';
+    const appFile = 'src/app.py';
+    const authUserId = 'class:src/auth_mod.py:User';
+    const userUserId = 'class:src/user_mod.py:User';
+    const authSaveId = 'method:src/auth_mod.py:save';
+    const userSaveId = 'method:src/user_mod.py:save';
+
+    ctx.symbols.add(authModFile, 'User', authUserId, 'Class');
+    ctx.symbols.add(userModFile, 'User', userUserId, 'Class');
+    ctx.symbols.add(authModFile, 'save', authSaveId, 'Method', {
+      ownerId: authUserId,
+      returnType: 'bool',
+    });
+    ctx.symbols.add(userModFile, 'save', userSaveId, 'Method', {
+      ownerId: userUserId,
+      returnType: 'bool',
+    });
+    // BOTH files imported by app.py — creates real ambiguity in tiered pool.
+    ctx.importMap.set(appFile, new Set([authModFile, userModFile]));
+    // Alias: `auth` points to auth_mod.py.
+    ctx.moduleAliasMap.set(appFile, new Map([['auth', authModFile]]));
+
+    // Call `auth.User.save(user)` — receiverName is `auth` (matches alias),
+    // receiverTypeName is `User` (the class). This is the class-as-receiver
+    // static-style pattern parse-worker emits when it sees `auth.User.save(x)`.
+    const calls: ExtractedCall[] = [
+      {
+        filePath: appFile,
+        calledName: 'save',
+        sourceId: 'Function:src/app.py:run',
+        argCount: 1,
+        callForm: 'member',
+        receiverName: 'auth',
+        receiverTypeName: 'User',
+      },
+    ];
+
+    await processCallsFromExtracted(graph, calls, ctx);
+
+    const rels = graph.relationships.filter((r) => r.type === 'CALLS');
+    // Module alias narrows to auth_mod.py. Without it the dispatcher would
+    // null-route because both User classes own a `save` method and there's
+    // no heritage or overload signal to pick between them.
+    expect(rels).toHaveLength(1);
+    expect(rels[0].targetId).toBe(authSaveId);
+  });
+
+  it('constructor overload disambiguation: same-arity ownerless constructors picked via preComputedArgTypes', async () => {
+    // Codex SM-19 adversarial review Finding 2: When two homonym constructors
+    // across different files have the same arity but different parameter types,
+    // `resolveStaticCall` correctly bails (step 3 ambiguity → step 4 bail because
+    // the tiered pool contains Constructor nodes). Before this fix the dispatcher
+    // then fell through to `singleCandidate` which also bailed because two
+    // constructors survive arity filtering. With overload disambiguation after
+    // `resolveStaticCall`, `preComputedArgTypes` picks the string overload.
+    const userFile = 'src/models/User.ts';
+    const repoFile = 'src/models/Repo.ts';
+    const appFile = 'src/app.ts';
+    const userClassId = 'Class:src/models/User.ts:User';
+    const repoClassId = 'Class:src/models/Repo.ts:User';
+    const userCtorId = 'Constructor:src/models/User.ts:User(string)';
+    const repoCtorId = 'Constructor:src/models/Repo.ts:User(number)';
+
+    ctx.symbols.add(userFile, 'User', userClassId, 'Class');
+    ctx.symbols.add(repoFile, 'User', repoClassId, 'Class');
+    ctx.symbols.add(userFile, 'User', userCtorId, 'Constructor', {
+      ownerId: userClassId,
+      parameterCount: 1,
+      parameterTypes: ['string'],
+    });
+    ctx.symbols.add(repoFile, 'User', repoCtorId, 'Constructor', {
+      ownerId: repoClassId,
+      parameterCount: 1,
+      parameterTypes: ['number'],
+    });
+    ctx.importMap.set(appFile, new Set([userFile, repoFile]));
+
+    const calls: ExtractedCall[] = [
+      {
+        filePath: appFile,
+        calledName: 'User',
+        sourceId: 'Function:src/app.ts:main',
+        argCount: 1,
+        callForm: 'constructor',
+        argTypes: ['string'],
+      },
+    ];
+
+    await processCallsFromExtracted(graph, calls, ctx);
+
+    const rels = graph.relationships.filter((r) => r.type === 'CALLS');
+    expect(rels).toHaveLength(1);
+    expect(rels[0].targetId).toBe(userCtorId);
+  });
+
+  it('constructor overload disambiguation: null-routes when disambiguation cannot pick unique survivor', async () => {
+    // Control test for Finding 2 fix: when `preComputedArgTypes` does not
+    // match any candidate uniquely, the dispatcher must null-route rather
+    // than pick arbitrarily. Preserves SM-10 R3.
+    const userFile = 'src/models/User.ts';
+    const repoFile = 'src/models/Repo.ts';
+    const appFile = 'src/app.ts';
+    const userClassId = 'Class:src/models/User.ts:User';
+    const repoClassId = 'Class:src/models/Repo.ts:User';
+    const userCtorId = 'Constructor:src/models/User.ts:User(string)';
+    const repoCtorId = 'Constructor:src/models/Repo.ts:User(string)';
+
+    ctx.symbols.add(userFile, 'User', userClassId, 'Class');
+    ctx.symbols.add(repoFile, 'User', repoClassId, 'Class');
+    // Both constructors take `string` — genuinely ambiguous.
+    ctx.symbols.add(userFile, 'User', userCtorId, 'Constructor', {
+      ownerId: userClassId,
+      parameterCount: 1,
+      parameterTypes: ['string'],
+    });
+    ctx.symbols.add(repoFile, 'User', repoCtorId, 'Constructor', {
+      ownerId: repoClassId,
+      parameterCount: 1,
+      parameterTypes: ['string'],
+    });
+    ctx.importMap.set(appFile, new Set([userFile, repoFile]));
+
+    const calls: ExtractedCall[] = [
+      {
+        filePath: appFile,
+        calledName: 'User',
+        sourceId: 'Function:src/app.ts:main',
+        argCount: 1,
+        callForm: 'constructor',
+        argTypes: ['string'],
+      },
+    ];
+
+    await processCallsFromExtracted(graph, calls, ctx);
+
+    const rels = graph.relationships.filter((r) => r.type === 'CALLS');
+    expect(rels).toHaveLength(0);
+  });
 });
 
 // ---- processAssignmentsFromExtracted: Phase 9 accumulator fallback ----

gitnexus/test/unit/symbol-table.test.ts

@@ -1753,14 +1753,15 @@ describe('resolveCallTarget thin dispatcher (SM-19)', () => {
     ctx = createResolutionContext();
   });
 
-  it('module alias homonyms: thin dispatcher returns null (no D1-D4 fuzzy path)', () => {
+  it('module alias homonyms: dispatcher resolves via module-alias narrowing to aliased file', () => {
     // Python-style: `import auth; auth.User.save()` where BOTH auth.py and
     // other.py define a `User` class with a `save` method.
     //
-    // Before SM-19, resolveCallTarget had D1-D4 fuzzy widening that could
+    // Codex SM-19 adversarial review Finding 1: the thin dispatcher must
-    // disambiguate via module-alias narrowing. The thin dispatcher delegates
+    // consult module-alias narrowing for typed member calls BEFORE falling
-    // to resolveMemberCall which sees two homonym Users and correctly returns
+    // through to owner/file-scoped resolvers. With both homonym files
-    // null (genuine ambiguity — no fuzzy path to break the tie).
+    // imported, owner-scoped resolution sees genuine ambiguity and the only
+    // remaining disambiguation signal is the alias on `call.receiverName`.
     ctx.symbols.add('src/auth.py', 'User', 'class:auth:User', 'Class');
     ctx.symbols.add('src/auth.py', 'save', 'method:auth:User:save', 'Method', {
       returnType: 'None',
@@ -1785,9 +1786,9 @@ describe('resolveCallTarget thin dispatcher (SM-19)', () => {
       ctx,
     );
 
-    // Thin dispatcher delegates to resolveMemberCall which returns null for
+    // Module-alias narrowing picks auth.py's save, not other.py's.
-    // genuine homonym ambiguity (both Users own `save`).
+    expect(result).not.toBeNull();
-    expect(result).toBeNull();
+    expect(result?.nodeId).toBe('method:auth:User:save');
   });
 
   it('overloadHints ignored for member calls — resolveMemberCall resolves directly', () => {